Description
Original instructions
About us
Using the block
Actuators are driven not only by analog quantities, but also through binary actuating signals. The conversion of analog values into binary output signals is achieved for example, through pulse width modulation (PWM) or pulse duration modulation (PDM).
The actuator adjusted average energy (actuator energy) should be in accord with the modulation block's analog input value (IN).
Function description
The function block PDM converts analog values into digital output signals.
In the function block PDM, a 1 signal of constant duration is output within a variable cycle time which depends on the analog value X. The adjusted average energy corresponds to the quotient of the fixed duty cycle t_on and the variable cycle time period.
In order that the adjusted average energy also corresponds to the analog input variable IN, the following must apply:
NOTE: This function block performs an internal initialization in the first program cycle after a warm start or cold start (e.g. application download or power cycle) of the PLC program.
Due to this, you have to make sure that the function block is invoked in the first program cycle. In case of inkoving the function block in a later program cycle, the internal initialization will not be performed and the ouputs may deliver wrong values.
WARNING
UNEXPECTED OUTPUT BEHAVIOUR
Make sure that the function block is always invoked in the first program cycle.
Failure to follow these instructions can result in death, serious injury, or equipment damage.
EN and ENO can be configured as additional parameters.
General information about the actuator drive
In general, the binary actuator drive is performed by two Boolean signals Y_POS and Y_NEG. On a motor the output Y_POS corresponds to the signal "clockwise rotation" and the output Y_NEG the signal "counter-clockwise rotation". For an oven the outputs Y_POS and Y_NEG could be interpreted as corresponding to "heating" and "cooling".
Should the actuating drive in question be a motor, it is possible that to avoid overtravel for non-self-locking gearboxes, a brake pulse must be output after the engage signal.
In order to protect the power electronics, there must be a pause time t_pause after switching on t_on and before the brake pulse t_brake so as to avoid short circuits.
Formula
For correct operation when setting parameters the following rules should be observed:
and
Representation in FBD
Representation:
Representation in LD
Representation:
Representation in IL
Representation: 
CAL PDM_Instance (X:=InputVariable, R:=ResetMode, 
    PARA:=Parameter, Y_POS=>Positive_X_ValueOutput, 
    Y_NEG=>Negative_X_ValueOutput)
Representation in ST
Representation: 
PDM_Instance (X:=InputVariable, R:=ResetMode, 
    PARA:=Parameter, Y_POS=>Positive_X_ValueOutput, 
    Y_NEG=>Negative_X_ValueOutput) ;
PDM parameter description
Description of input parameters:
Parameter
Data type
Description
X
REAL
Input variable
R
BOOL
Reset mode
PARA
Para_PDM
Parameter
Description of output parameters:
Parameter
Data type
Description
Y_POS
BOOL
Output for positive X values
Y_NEG
BOOL
Negative X value output
Parameter description Para_PDM
Data structure description
Element
Data type
Description
t_on
TIME
Pulse duration (in s)
t_pause
TIME
Pause time (in s)
t_brake
TIME
Braking time (in s)
pos_up_x
REAL
Upper limit for positive X
pos_t_min
TIME
Minimum cycle time for Y_POS (where x = pos_up_x) (in s)
pos_lo_x
REAL
Lower limit for positive X
pos_t_max
TIME
Maximum cycle time for Y_POS (where x = pos_lo_x) (in s)
neg_up_x
REAL
Upper limit for negative X
neg_t_min
TIME
Minimum cycle time for Y_NEG (where x = -neg_up_x) (in s)
neg_lo_x
REAL
Lower limit for negative X
neg_t_max
TIME
Maximum cycle time for Y_NEG (where x = -neg_lo_x) (in s)
Runtime error
An error message is returned if
NOTE: For a list of all block error codes and values, see CLC_PRO.